In various household appliances, lighting devices and industrial products, the application of non-linear loads are very widespread. For example, non-linear loads may be applied to microwave oven magnetrons, induction coils of induction cookers, various gas discharge lamps, induction heating coils, and so on. These products are usually operated in a wide range of input voltages or a wide range of loads. Generally, a constant-voltage control mechanism or a constant-current control mechanism is widely used in a general power supply apparatus. If the constant-voltage control mechanism or the constant-current control mechanism is applied to the products with the non-linear loads, the input power or the output power can not be effectively controlled. For maintaining stable energy output in any operating condition, a constant-power control mechanism is gradually adopted in the products with the non-linear loads.
In a conventional constant-power control mechanism, a voltage signal and a current signal are firstly detected, and these two signals are provided to a micro-controller unit (MCU) or a digital signal processor (DSP) for calculation. Since the power calculation needs multiplication or more complex calculation such as root-mean-square (RMS), the power calculation may consume many computing resources of the micro-controller unit or the digital signal processor. Under this circumstance, some other important scheduled tasks are adversely affected.
For solving the above drawbacks, an external multiplier chip is used to reduce the workload. Although an additional multiplier chip can achieve the purpose of reducing the workload, the additional multiplier chip may increase manufacturing cost.
Therefore, there is a need of providing an improved power control circuit and a power supply system using the same in order to reduce the workload of the micro-controller unit or the digital signal processor and reduce the manufacturing cost.